Theresa May cancelled an aerial surveillance programme designed to stop migrants crossing the Channel into Britain to save money despite warnings from a former security minister, the Telegraph can disclose.

The Home Secretary in January agreed to scrap a £4million surveillance contract despite being told by Baroness Neville-Jones, a former security minister and chairman of the Joint Intelligence Committee, that it was a risk to Britain’s border security.

The Home Office on Tuesday announced that around six new vessels would be brought into service to patrol British coastal waters.

However, the plans were immediately labelled a “joke” by Conservative MPs after it emerged that all of the boats will not be fully operational until the end of 2017.

Mrs May in January cancelled the contract with Cobham, a major aviation services company, providing round-the-clock aerial surveillance of Britain’s borders.

In a letter to the Home Secretary seen by the Telegraph, Baroness Neville-Jones said: “Cobham are well aware that their service is not the only way in which aerial surveillance can be provided.

"They do point out however, legitimately in my view, that if the intention is for the Border Force to rely from January solely on services that can be procured on an ad hoc basis under the MMO's Framework Agreement, this is likely to lead to reliance on less capable aircraft with much less experienced and practised crews - if indeed there is any availability at all when needed.”

In a response Philip Duffy, Chief Operating Officer of the Border Force, said that the Government has to "ensure value for money"

We are taking a gamble that nothing will ever happen in our seas and that is a risky view to take given the dangerous world we are inLord West

He said: “As you are aware, there are other forms of aerial surveillance available across Government which will provide the required level of capability, and it is also incumbent upon Border Force to continue to explore new and emerging technologies available in the market place.”

Frank Hurst, a former head of maritime operations at HM Customs and Excise, said that the decision to end the air surveillance contract was "short sighted".

He said that the surveillance has been in use for more than 20 years and had proved "extremely helpful" in spotting vessels.

He said: "You can cover a huge amount of ground. It was extremely helpful in operations, especially when we had a particular target.

"I was very disappointed to see that the contract was cancelled. It seems short-sighted because we built up a lot of expertise over the years."

Christopher Chope, the Tory MP for Christchurch who also raised concerns about the cancelling of the contract to the Home Secretary, said: “Aerial surveillance is a key part of our capability. This contract was cancelled not because of need but in order to save money.”

Philip Davies, a Conservative MP, said that the delay in introducing the new vessels is "a joke".

He said: "It simply isn't good enough. It is the equivalent of shutting the stable door after the horse has bolted.”